High performance ink jet nozzle

ABSTRACT

An improved ink jet nozzle structure utilizes an ink supply chamber having a source of ink under pressure connected thereto and a nozzle passage provided with a jewel nozzle having an orifice with a low aspect ratio and defined by an abrupt or sharp entrance on the chamber side.

United States Patent [191 Gordon, III

HIGH PERFORMANCE INK JET NOZZLE Inventor: William M. Gordon, III, Endwell,

Assignee: International Business Machines Corporation, Armonk, NY. Filed: Nov. 29, 1972 Appl. No.: 310,297

US. Cl 346/140, 239/601, 346/75 Int. Cl. G0ld 15/18 Fieldof Search 346/75, 140; 239/596, 601,

References Cited UNITED STATES PATENTS Danielsson 239/596 X July 9, 1974 2,600,426 6/1952 Paul 346/!40 ux 3,28l,86() lO/l966 Adams clal r 346/75 3,683,2l2

8/1972 Zoltan 346/l40 X Primary Examiner-Joseph W. Hartary Attorney, Agent, or FirmFrancis V. Giolma [57] ABSTRACT An improved ink jet nozzle structure utilizes an ink supply chamber having a source of ink under pressure connected thereto and a nozzle passage provided with a jewel nozzle having an orifice with a low aspect ratio and defined by an abrupt or sharp entrance on the chamber side.

1 Claim, 4 Drawing Figures VIBRA/TING TRANSDUCER DESCRIPTION OF THE PRIOR ART Ink jet nozzles are known such as shown in the Adams US. Pat. No. 3,334,350 which issued Aug. 1, 1967 wherein a watch jewel is used-for an ink nozzle, and also as shown in the Colecchi US. Pat. No. 3,512,172 which issued on May 12, l970.

SUMMARY OFTHE INVENTION This invention relates generally to ink jet printers and it has reference in particular to an improved ink jet nozzle structure for an ink jet printer.

More specifically it is an object of the invention to provide an ink jet nozzle structure which has a more uniform ink drop formation.

Another object of the invention is to provide for minimizing the production of satellite ink drops in an ink jet printer.

Yet another object of this invention is to provide for using a nozzle in an ink jet printer having a low aspect ratio.

It is also an object of this invention to provide for using a jewel nozzle in an ink jet nozzle structure having both a low aspect ratio and a sharp entrance edge.

Still another object of this invention is to provide for using a jewel nozzle in an ink jet nozzle structure havingan aspect ratio of unity or'less.

It is also an important object of this invention to provide for using a jewel nozzle in an ink jet nozzle structure .having both a low aspect ratio and a sharp entrance edge with all surfaces adjacent and in the opening being hydraulically smooth.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawing.

7 DESCRIPTION OF THE DRAWING I In the drawing v FIGS. la, lb, and 1c are a schematic showing of curves illustrating the velocity profile changes during drop formation with nozzles of different aspect ratios.

FIG. 2 is a schematic showing of an ink jet nozzle structure embodying the invention in one of its forms.

FIG. 3 is an enlarged cross-sectionalview of the jewel nozzle of FIG. 1 showing further details of the invention and I FIG. 4 is a front side elevation view of the jewel nozzle of FIG. 3 reduced in size.

DESCRIPTION OF A PREFERRED EMBODIMENT small or satellite drops. The diameter variations previously mentioned will occur and form drops naturally.

Periodic variations can be produced by applying a periodic driving force as described in US. Pat. No. 3,596,275 which issued on July 27, I971 to Richard G. Sweet and drop charging may also be provided as described therein. However, the thin regions which form satellites will still form unless proper precautions are taken. The proper precautions are to match the velocity profiles of the free jet stream and a drop as nearly as possible and to have laminar flow atthe entrance to the nozzle.

For ink jet printers, these two conditions can be met by using nozzles with aspect ratios (hole length/hole di ameter) on the order of 0.5:1-lzl and by making all surfaces leading up to the nozzle as well as the nozzle itself hydraulically smooth. A surface can be considered hydraulically smooth if any projection or depression denoted by K is less than or equal to the thickness of the boundary layer. This is defined by the relationship K, is equal to or less thar SV/U V SIN where 1/ equals the kinematic viscosity U equals mean velocity of the fluid stream and N equals the Reynolds number.

When a column of liquid leaves a nozzle its velocity profile must change from what it was when it left the nozzle to that of a drop or something that approximates that of a drop before a drop can form. Accordingly, there is a range of profiles over which drop formation can occur. 7

Referring to FIGS. la through 1c it will be seenfrom the curves 10ag, l2a-f and l4a-g that the amount of time which lapses before drop breakoff occurs should also be longer with the fully developed profile. These curves indicate that the velocity at the edges of a drop which is forming is less than at its center as it leaves the nozzle and the velocity of the edges and center approach a common value at the moment of drop formation. For lower aspect ratios this result is reached sooner and at a lesser distance from the nozzle as shown by the curves for aspect ratios of a 3, 0.5 and 0 respectively.

Although turbulent flow has a relatively flat velocity profile there is a considerable amount of rotation which makes this condition unstable and undesirable. The desired condition is to go from a low velocity with laminar flow to a high velocity with incompletely developed laminar flow through the use of a sharp-edged orifice 32 as shown in FIG. 3. The sharp-edged orifice also has the advantage of providing an initial symmetrical disturbance in the radial directions and stronger coupling between the vibrating structure and the fluid by minimizing damping in the radial direction.

Referring to FIG. 2 the reference numeral 16 denotes generally an ink nozzle structure comprising a supply chamber 18 having attached thereto at one end a vibrating mechanism 20 such as a piezo electric crystal or magneto strictive transducer or the like. The chamber 18 has a supply tube 22 connected thereto for supplying ink thereto under a pressure of 10 to pounds per square inch for example. The right hand wall 24 of the chamber 18 has a recess 26 therein with a shoulder portion 28 providing a seat for a jewel nozzle 30 which may be secured therein by cementing staking or rolling the edge 31. The jewel nozzle 30 may be-a natural or 3 is provided with an orifice or opening 32 therethrough opening into a conical depression 34 defined by outwardly flared surface portions 36.

Referring to FIG. 3 it will be seen that the jewel orifice or nozzle 30 has a sharp edged portion 40 immediately adjacent the entrance of the orifice 32. The length of the orifice L is relatively short compared to the diameter of the orifice D, so that the aspect ratio L/D is low, preferably in the range of 0.5 to 1.0. The surface portion 42 of the nozzle 30 adjacent the orifice 32 is polished so as to be hydraulically smooth and must be both flat and perpendicular to the axis of the orifice 32. The corner 40 must be sharp and devoid of any notches or ridges so as to avoid turbulence and impart a symmetrical velocity increase to the stream from a value V1 within the chamber 18 to a high velocity V2 with incompletely developed laminar flow. The sharp-edged orificealso has the advantage of providing an initial symmetrical disturbance in the radial direction as the stream issues from the orifice at the point 33 and a stronger coupling between the vibrating structure and the fluid by minimizing damping in the radial direction. The sides of the orifice 32 must be parallel and the length L of the orifice 32 should be in the range of D/2 to D where D is the diameter of the orifice for optimum performance. The flared opening 34 facilitates the use of a wire or other similar object to unclog or clean the nozzle in the event of a stoppage. The nozzle 30 may comprise for example a synthetic sapphire watch jewel having an orifice on the order of .001 .002 inches and a length L of .005 .001 inches by way of example.

From the above description and accompanying drawing it will be apparent that an improved ink jet nozzle is provided which reduces significantly the number of satellite drops formed during the drop forming process. By utilizing a low aspect ratio of orifice length to diameter the drop breakoff distance is shortened or a lower head driving voltage may be used to achieve the same breakoff distances as in other nozzles. Accordingly, a more uniform ink drop production is achieved with fewer .satellites and higher print quality.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In an ink drop nozzle apparatus comprising a hollow member to which ink is applied under a pressure of from 10 to pounds per square inch, said member having a passage through which ink flows for the purpose of producing a succession of uniformly spaced substantially uniform ink drops, the improvement in said nozzle apparatus comprising a jewel nozzle positioned in said passage and having an orifice therethrough with a diameter in the range of .001 .002 inches and a length of ;OOO5 .001 inches thus providing an aspect ratio of Hole Length/Hole Diameter which is less than 1.0,

and having a sharp entrance edge defined by a plane surface surrounding said entrance edge which is perpendicular to the axis of said orifice and an outwardly flared exit surface immediately adjacent said orifice, said orifice, plane surface, and entrance edge being hydraulically smooth so as to provide with said aspect ratio incompletely developed laminar flow of said ink, whereby the formation of satellite ink drops between drops is minimized. 

1. In an ink drop nozzle apparatus comprising a hollow member to which ink is applied under a pressure of from 10 to 100 pounds per square inch, said member having a passage through which ink flows for the purpose of producing a succession of uniformly spaced substantially uniform ink drops, the improvement in said nozzle apparatus comprising a jewel nozzle positioned in said passage and having an orifice therethrough with a diameter in the range of .001 - .002 inches and a length of .0005 - .001 inches thus providing an aspect ratio of Hole Length/Hole Diameter which is less than 1.0, and having a sharp entrance edge defined by a plane surface surrounding said entrance edge which is perpendicular to the axis of said orifice and an outwardly flared exit surface immediately adjacent said orifice, said orifice, plane surface, and entrance edge being hydraulically smooth so as to provide with said aspect ratio incompletely developed laminar flow of said ink, whereby the formation of satellite ink drops between drops is minimized. 